Testicular torsion is a medical emergency and can cause permanent loss of spermatogenesis. Torsion causes testicular ischemia. Conventional treatment consists of surgically reducing the torsion and fixing the testis in position. Blood flow returns in timely repairs, but even in these cases the testis often experiences significant atrophy. No medical supplemental treatments are currently available. Understanding the biological mechanisms underlying this atrophy is important in determining treatments to rescue the torsed testis. It is known from previous research in our laboratory using the rat model that torsion followed by torsion repair (TTR) can permanently eliminate spermatogenesis in the affected testicle and that this is due to increased germ cell apotosis (GCA). GCA is induced by an increase in reactive oxygen species (ROS) causing oxidative stress. ROS rises in conjunction with increasing neutrophils in the testis after torsion repair and neutrophils accumulate due to an increase in vascular E-selectin expression. The present proposal seeks to extend these studies of the pathway to GCA after torsion repair. Specific Aim 1 examines further the vascular response to TTR and seeks to define the molecules involved in regulating E-selectin expression. We will test the hypothesis that E-selectin expression after TTR is regulated through the cytokine - stress related kinases pathway. Specific Aim 2 deals with the pathway to GCA within germ cells. TTR causes ischemia followed by reperfusion. Most investigations have studied the effects of reperfusion, but Specific Aim 2 will investigate whether a specific transcripion factor, HIF-1, is induced during the ischemia and will test the hypothesis that HIF-1 plays a role in GCA through the stabilization of p53 and subsequent upregulation of Bax, a proapoptotic molecule in the mitochondrial pathway to apoptosis. Oxidative stress is induced by neutrophil invasion but mitochondria are important in these studies for three reasons: 1) they are key to an important pathway to apoptosis responding to oxidative stress 2) after torsion repair they could be an intracellular source of ROS, and 3) their dysfunction could lead to energy depletion. Specific Aim 3 will examine the mitochondrial response to TTR and test the hypothesis that torsion-induced oxidative stress causes differential mitochondrial dysfunction in different germ cell maturation states. Specific Aim 4 proposes to use information developed in the previous specific aims and elsewhere to inhibit specific steps of the pathway to GCA and to test the hypothesis that interference with specific steps in the path will provide significant rescue of the testis after TTR. It is likely that these investigations will be relevant to other forms of oxidative stress inducing testicular dysfunction.